Discussion summary: We discussed Maillard, RA et al. "ClpXP Generates Mechanical Force to Unfold and Translocate its Substrates", Cell 145, 459, 2011. A single-molecule study using optical tweezers showed that ClpX is able to generate mechanical force to unfold substrates, and favored a power-stroke mechanism for the motor. Another interesting observation was that the group was able to observe a well-defined intermediate in the unfolding of GFP by ClpX and define the location of the intermediate. This is an important step forward in research on AAA+ unfoldases.